Various manually driven carrier vehicles, for example, hand trucks and carts are commonly used for moving objects that are otherwise inconvenient for a person to carry due to size and/or weight. Often, these hand trucks and carts are foldable for ease of storage and transportation when not in use. They typically have a telescoping or folding handle, a folding chassis, and wheels either set into a predetermined position or pivotable around longitudinal axes of chassis frame. Such carriers have limited capability to traverse rough or uneven terrain because the portability requirement in the folded state limits the range of possible wheel diameters, which, in turn, limits suspension responsiveness. This is because the efforts of moving a cart at a given coefficient of friction depend inversely on a ratio of wheel to axle diameters and the wheel diameter to height of an obstacle. Other carriers, besides having a telescoping or folding handle and a folding chassis, utilize removable wheels of relatively large size as means to improve terrain trafficability, yet reduce overall dimensions in the folded state. However, removing the wheels requires additional time and complicates handling and storage of the carrier, particularly after use on wet or muddy surfaces.
Thus, conventional folding carts and hand trucks, in addition to be able to transport a predetermined load, are designed primarily for convenient handling and portability when folded. However, these known carriers, independently of any trade-offs between the convenience of use and the size in the folded state, are difficult to handle when moving over an irregular terrain, curbs, stairs, and other obstacles.
Carrier chassis better capable of dealing with uneven surfaces and convenient to store or transport when folded are disclosed in U.S. Pat. No. 8,541,059 and U.S. Pat. No. 9,187,106, the entire contents of which are hereby incorporated by reference. However, the hand truck taught in U.S. Pat. No. 9,187,106, due to common for hand trucks requirement to have the platform at and the wheels above a ground level in unfolded state, comprises a segment of Maltese cross mechanism, which negatively affects performance and increases dimensions and weight of the device as well as complicates the design process due to nonlinear relation between velocities of parts during folding and unfolding.
Therefore, it is desirable to provide a simplified foldable hand truck capable of moving over a rough terrain, including curbs, stairs, and spongy soil and be foldable relatively flat without disassembling.